Recently, diverse researches on providing multiple multimedia services including a voice service and transmitting high speed data while maintaining high quality in a radio communication environment are being conducted. In particular, technique for a multi-input multi-output (MIMO) communication system using a plurality of channels in a spatial area is being rapidly developed.
First, a general MIMO technique will now be described.
In brief, a MIMO refers to a method for improving data transmission and reception efficiency by using multiple transmission antennas and multiple reception antennas, shedding a system in which a single transmission antenna and a single reception antenna are used. Namely, the MIMO refers to a technique of seeking an increase in the capacity of data transmission or improvement of performance by using multiple antennas at a transmission end or at a reception end of a wireless communication system.
A multi-input multi-output technique (or a multi-antenna technique) is an application of a technique of collecting data fragments received by multiple antennas for a completion, rather than relying on a single antenna path for receiving a single entire message. Accordingly, a data transmission rate can be improved or an application range of the system can be increased over a particular data transmission rate.
In the MIMO communication system, a base station and mobile stations use a codebook in order to properly cope with a channel environment. A particular space can be quantized to a plurality of codebooks, and a plurality of codewords generated by quantizing the space according to a certain reference can be stored in the base station and mobile stations. Here, each codeword may be a vector or a matrix depending on the dimension of a channel matrix.
Namely, each mobile station selects one matrix or vector corresponding to channel information from among matrixes or vectors included in the codebook according to a channel formed between the base station and each mobile station. Also, each base station can recognize channel information by receiving the matrix or vector selected by each mobile station by using the codebook. Also, the selected matrix or vector may be beamformed by the base station or may be used to transmit data by using multiple antennas. Thus, in the MIMO communication system, it is very important to properly design a codebook in order to effectively transmit data.
Thus, as mentioned above, how well a codebook is designed causes a big difference for a data transmission efficiency, an optimized codebook needs to be designed to effectively transmit data.
In general, a considered communication environment has various channel characteristics and frequency bands. However, in the related art, an antenna topology and configuration with respect to a base station or a mobile station are fixed, so although the same codebook is used, the same performance is not guaranteed according to the antenna topology and configuration of the base station and the mobile station, causing a problem in that the overall performance is degraded.